What does "18 Innings" Rule mean?

"18 Innings" Rule meaning in Urban Dictionary

In baseball groups, a term regularly deliver a brief texting. The guideline indicates the unwillingness of a spectator/diehard fan to leave from a ballgame before its conclusion, regardless of what number of innings it may take to do so beyond the standard nine innings of this sport.Origin for the term isn't understood, nor the explanation for selecting the number 18, except to simply note the size of two regular games. Potentially, extra innings can increase indefinitely past 18, but it's unusual.